1. Field of the Invention
This invention relates broadly to an apparatus for determining one's position on the Earth. More particularly, this invention relates to a sight reduction apparatus for determining one's position using measurements done with a sextant.
2. State of the Art
Sextants are commonly used to locate one's position, especially at sea. Current technology to find one's position using a sextant first requires the user to measure the sextant altitude of at least two celestial bodies. The celestial bodies are located in an imaginary circle representative of all the points on Earth from which one could measure the altitude of the celestial bodies. Second, incorporating his/her sextant readings, current time and date, and one's assumed position into a series of multiple look-up tables, a "line of position" with respect to each celestial body is derived. The lines of position are small segments of the imaginary circle close to the assumed position. One's position is found at the intersection of two lines of position, or at the center of a triangle formed at the intersection of three lines of position. Nevertheless, such a method of locating one's position is accompanied by the error inherent in stating one's assumed position. This error is amplified when the angle between any two lines of position is small, e.g., less than approximately thirty degrees.
A more reliable manner of determining one's position is required for an apparatus used as a back up navigation mechanism of a boat's electronic navigation system. Likewise, lifeboat navigation requires a manner of finding navigational fixes which do not depend on knowledge of one's assumed position. When on a life boat at sea, especially for a few days, the position of the boat is far from certain.
In addition, knowledge of one's position in terms of intersecting lines of position is not nearly as preferable as knowledge of one's position in terms of latitude and longitude.